1. Field
The following description relates to a fault tolerant apparatus for an independent controlled steering in a four wheel system, particularly a fault tolerant apparatus for an independent controlled steering in a four wheel system which can stabilizes a vehicle body through actively adjusting a steering angle of a vehicle and a velocity of a vehicle according to a breakdown environment and a vehicle driving road environment. Further, a fault tolerant apparatus for an independent controlled steering in a four wheel system that may assist a safe driving environment by adjusting a turning function adoptively to a surrounding road environment.
2. Description of Related Art
In general, four wheel drive vehicles are designed such that the inscribed circles of the steering angles of the wheels make coaxial circles in turning so that the turning radii of the wheels keep constant. However, when one or more steering systems for the wheels break, the centers of the inscribed circles of the steering angles cannot converge on one point, such that large stress is applied transversely to the vehicles that are rigid bodies; therefore, the structural safety of the vehicles is considerably deteriorated and it exerts critical influence on the safety of the driver in the vehicles.
Accordingly, studies about the technology of efficient steering control of a four wheel drive vehicles which can improve structural safety of a vehicle and contribute to the safety of a driver have been conducted.
Patent Document 1 relates to an electric steering system for a vehicle, disclosing a technology of allowing stable steering by using the existing devices or components when there is a fault in a steering-driving motor in the steering system.
In detail, there is disclosed in Patent Document 1 a technology of controlling the braking force from brake systems to have a calculated value by sensing a fault in a steering-driving motor from the relationship between the amounts of input and output currents of the steering-driving motor and the rack displacement of the turning angle of a steering wheel, using a steering-driving motor sensing unit, and by calculating the braking force of the brake systems for the wheel such that the traveling direction of a vehicle changes in proportion to the turning direction and angle of the steering wheel, when there is a fault in the steering-driving motor.
Patent Document 2 discloses a technology that calculates torsion calculated from a steering angle detected by a steering angle sensor and the torque of a motor, calculates the difference between the equivalent steering angular speed and the steering angular speed of the motor including the torsion with reference to the torsion, and turns off the power, when the difference exceeds a threshold value.
In detail, in Patent Document 2, there is disclosed a technology that compensates for an error generated due to a torsional effect by calculating the correct equivalent steering angular speed including the torsional effect in response to a signal from a motor, using an ECU included in a fault sensing unit in a steering system, and increase safety in driving by turning off the power, when the difference between the equivalent steering angular speed and the steering angular speed exceeds a threshold value, that is, only when a problem is actually generated.
However, Patent Documents 1 and 2 disclose only the technology of controlling the turning direction and angle through braking, when there is a fault in a steering system, such that the turning radius of a vehicle cannot be controlled at the same time.